1. Field of the Invention
The present invention is related to personal computers and more particularly to a method and apparatus for determining and distributing computer system clocks.
2. Background Art
The flow of information through the internal circuits of a computer is synchronized by an electronic circuit called a clock that generates evenly spaced timing pulses at high speeds. IBM compatible personal computer (PC) systems are designed in a fully synchronous fashion with each component of the system being driven by a common clock. This requires distribution of a large number of low-skew clock signals throughout the system. In those circumstances where there are several clock speed choices a method of choosing the proper clock is provided.
The main hardware part of a personal computer (PC) is called a mother board which is a large printed circuit board that has plugged into it the computer's central processing unit (CPU), which is an INTEL brand or compatible microprocessor, memory, input/output (I/O) control, and microprocessor support chips. The mother board has expansion slots that receive add-in cards that plug into the expansion slots. The IBM PC architecture uses a MICROSOFT brand disc operating system (DOS) as the software program that controls the overall operation of the computer by instructing the computer what to do and when to do it.
A clock is provided on the mother board that runs at a speed that is appropriately matched to the speed of the central processing unit (CPU) that is plugged into the motherboard. If a socket is provided on the motherboard for a future CPU upgrade or other upgrade, an optional module can be plugged in. The module may contain a CPU that operates at a different and perhaps higher speed than the CPU that was originally supplied on the mother board. In this circumstance, the clock distribution circuitry on the mother board must be switched to the new clock.
The most common way of switching clocks is manually by human intervention. The person configuring the system is instructed to shut off power to the computer and to insert appropriate jumper wires on the mother board that select he proper clock. This method is subject to human error and cannot be performed automatically when the computer is turned on.
It is therefore an object of this invention to provide a method and apparatus to cause a PC motherboard to automatically detect that a new clock is present and configure itself appropriately to distribute the new clock.